1. Field of the Invention
This invention relates to a positioning table movable in a plane in the directions of the X-axis (the abscissa) and the Y-axis (the ordinate) of the coordinates disposed perpendicular to each other.
2. Description of the Prior Art
Positioning tables of the type under consideration have been widely used in assembling machines, machine tools, measuring apparatus, and like. A typical example of such positioning tables, as shown in FIG. 6, comprises an X-table 3 mounted on a bed 1 for sliding movement along a pair of roller guides 2, 2 provided respectively on opposite side portions of the bed 1. A Y-table 5 is mounted on the X-table 3 for sliding movement along a pair of roller guides 4, 4 in a direction perpendicular to the direction of movement of the X-table 3. A motor 6 is fixedly mounted on one end of the bed 1, and another motor 7 is fixedly mounted on one end of the X-table 3. The motor 6 is connected to the X-table 3 by a ball-screw rod (not shown), and the motor 7 is connected to the Y-table 5 by a ball-screw rod 8. Therefore, when the motor 6 is driven, the X-table 3 is moved relative to the bed 1, and when the motor 7 is driven, the Y-table 5 is moved relative to the X-table 3.
In the above conventional positioning table, since the driving forces are transmitted to the X- and Y-tables 3 and 5 through the ball-screw rods, positioning accuracies are not satisfactory because of backlashes. Further, the bed 1, the X-table 3 and the Y-table 5 are arranged in a three-layer manner, and the two motors 6 and 7 are projected from the sides of the positioning table. Therefore, the overall construction of the positioning table is rather bulky.